There is a widespread need for improving the accuracy of sample measurement systems such as those enabling e.g. a diabetes sufferer to know their blood sugar levels—i.e. the concentration of glucose in their blood.
Existing sample measurement systems use a measurement device which receives and takes measurement readings from a sampling plate spotted with a blood sample from a user. The sampling plate is often rectangular and is end-loaded with the blood sample. The blood sample, once loaded, is usually drawn into a sample zone having a number of sampling zones from which measurements are taken by the system.
Each sampling zone typically has its own particular contents. For example, the first sampling zone may have a glucose oxidase deposit within it, a second deposit comprising a mixture of glucose oxidase and a predetermined amount of glucose, while a third sampling zone may contain no deposit. As the blood sample is drawn over all three sampling zones, chemical reactions occur with the deposits in each sampling zone, resulting in discrete electrolytes. Each sampling zone bridges a corresponding pair of electrodes. A potential difference is established across each sampling zone, via the electrodes, when the sampling plate is inserted into an operating measurement device. Electric current readings for each sampling zone then provide measurements necessary to assess the blood sugar (glucose) levels. For instance, the first sampling zone may give the primary measurement, whereas the second sampling zone may provide a degree of calibration since a known quantity of glucose was already present there. The third zone may give a final check by accounting for the non-glucose contribution to the measurements in the first and second sampling zones.
However, in spite of these calibrations and final checks, error margins in such blood glucose readings are still high. Indeed, blood glucose levels are strongly influenced by the fluctuating and transient glucose levels in the plasma of the blood sample, which may not be representative of the long-term blood glucose levels of the patient and may, rather, simply indicate a recent transient rise or drop in blood glucose levels within the blood plasma of the patient e.g. due to recent food consumption of other short-term environmental factors.
The present invention aims to address this.
Blood plasma is the liquid component of blood in which the blood cells in whole blood are normally suspended. Blood plasma typically constitutes about 55% of the total volume of the blood. It is the extracellular fluid part of blood and is mostly water but contains dissolved glucose and other contents.
The volume percentage of red blood cells in blood is known as the haematocrit (HCT). Other terms for this are the packed cell volume (PCV) or erythrocyte volume fraction (EVF). Haematocrit is normally about 45% for men and 40% for women. The haematocrit is typically calculated by multiplying the red blood cell count in a blood sample by the average cell volume, then dividing the result by the whole blood sample volume.
Glycated haemoglobin (a.k.a. haemoglobin A1c, HbA1c, or just A1c) is a form of haemoglobin measured primarily to identify the average plasma glucose concentration over prolonged periods of time. It is formed in a non-enzymatic glycation pathway by hemoglobin's exposure to plasma glucose. Normal levels of glucose produce a normal amount of glycated hemoglobin. As the average amount of plasma glucose increases, the fraction of glycated hemoglobin increases. This serves as a marker for average blood glucose levels over the previous months prior to the measurement. Liquid chromatography and capillary electrophoresis are two ways of measuring glycated haemoglobin (HbA1c). Both methods are complex, expensive and wholly unsuited for easy and simple implementation by a patient.